Compensated reed mounting



March 14, 1950 D. E. NOBLE 2,500,372

COMPENSATED REED MOUNTING Filed Aug. 21, 1947 +17 14 M 22 l J5 10 j I i AAAAAAAA )v 1119/ E I I v v v v v v v I i 18 Z.

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Patented Mar. 14, 1950 UNITED STATES PATENT OFFICIE COMPENSATED REED MOUNTING Daniel E. Noble, Elmhurst, 111.,

assignor to Motorola, line, Chicago, 111., a corporation of Illinois 14 Claims.

This invention relates generally to vibrating members and more particularly to a vibrating reed and mounting therefor in which the mounting compensates for the natural frequencytemperature characteristics of the reed.

In the prior art many attempts have been made to provide vibrating units in which the frequency of vibration is independent of the temperature to which the unit is subjected. Such vibrating units have application to musical instruments such as organs, to signaling systems such as selective calling systems for communication equipment, and in many other instances. Vibrating members have been made of materials which are affected only slightly by temperature and of a plurality of materials in which the temperature characteristics of one material compensates for the temperature characteristic of another, but such units have been relatively expensive and have not been entirely satisfactory.

It is, therefore, an object of the present invention to provide a simple vibrating unit arranged to operate on a particular frequency which is substantially independent of the temperature to which the unit is subjected.

A further object of this invention is to provide a mounting for a vibrating member which supports the member in such a manner to compensate for the natural characteristics of the member to change its natural frequency with change in temperature.

A feature of this invention is the provision of a constant frequency vibratory unit including a member which changes dimensions with change in temperature to thereby change its natural frequency of operation, and mounting means for the member which supports the same so that a variable portion of the member is free to vibrate.

A further feature of this invention is the provision of a vibrating reed, the natural frequency of which changes with temperature due to the temperature coefficient of expansion of the material of which it is made and the change in elasticity thereof, and a mounting made of a material having a large temperature coefiicient of expansion and arranged to support the reed so that the portion thereof free to vibrate changes with temperature to compensate for the natural characteristics of the reed.

Further objects, features and advantages will be apparent from a consideration of the following description taken in connection with the ac companying drawings in which:

Fig. 1 illustrates a vibrating unit in accordance With the invention;

Fig. 2 is a cross-sectional view along the lines 2--2 of Fig. 1 illustrating the construction of the clamp; and

Fig. 3 illustrates a modified mounting in accordance with the invention.

In practicing the invention there is provided a vibrating member such as a reed made of a material which expands with temperature and in which the elasticity changes with temperature, both of which factors cause the natural frequency of vibration of the reed to decrease with rise in temperature. A mounting is provided for the reed for supporting one end thereof so that the remaining portion of the reed is free to vibrate about a point along the length of the reed. The mounting is arranged to support the reed so that as the material from which the mounting is made expands or contracts, the length of the vibrating portion of the reed changes to change the frequency thereof. The material of the mounting is so chosen that the length of the free portion of the reed is adjusted to compensate for the temperature characteristics thereof so that the natural frequency of the portion free to vibrate is substantially constant through a relatively wide range of temperatures.

Referring now to the drawings, in Fig. 1 there is illustrated an elongated vibrating member or reed Ill which is supported on a mounting generally indicated as H. The mounting includes a base member 12, a top member 13, a spacer It and a clamp 15. The base and top members I2 and I3 are made of relatively rigid material so that they form a solid mounting for the vibrating reed. The end I8 of the reed may be rigidly secured to the members it and 13 as by solder IS. The spacer it holds the rear end of the top member l3 away from the reed with the front edge 16 of the member i3 engaging the reed. The edge 16 of the member l3 engages the reed ll] with sufficient pressure that the reed vibrates about this point. This pressure is provided by the clamp l5 which may be adjusted by changing the position of the screw i7 therein. The spacer it may be relatively thin being merely large enough to prevent clamping engagement of the top member 13 all along the surface of the reed. Such freedom from clamping engagement is necessary so that as the reed It changes lengths due to change of temperature the reed will be free to slide with respect to the member l2. On the other hand, the top member 13 must be relatively closely spaced to the reed all along the length thereof to prevent vibration of the por- 3 tion of the reed positioned between the clamping members.

Although the vibrating member and mounting therefor as above described are adaptable for use in many applications, such as in musical instruments, a unit is illustrated in Fig. 1 in a system applicable for use in signaling as in a selective calling system for either radio or wire communi cation systems. In Fig. l, a winding 20 is shown about the reed and a magnet 2| having a north pole 22 and a south pole 23 is shown at the outer end of the reed. The winding 20 is adapted to be connected to a signaling circuit in which currents of various frequencies may flow. It is apparent that if the reed If) is made of magnetic material a field will be set up therein by the current flowing in the winding 20 which will cooperate with the field produced by the magnet 2| to tend to cause vibration of the reed [0. When the frequency of the current flowing through the wind ing 20 corresponds to the natural frequency of the reed iii the vibration of the reed will build up and be sustained as long as the current fiows. A flexible contact 24 is secured to the end of the reed and cooperates with an adjustable fixed contact 25 which is supported adjacent thereto so that when the vibration of the reed H1 builds up to a predetermined value the Contact 24 will intermittently engage the contact 25. By making connection to the reed l and to the fixed contact 25 as by conductors 2B and 21, a circuit is provided which is intermittently closed by vibration of the reed Hi. This circuit can be utilized to exercise various standard controls and is, therefore, suitable for use in a selective signaling system to operate such a control when a particular frequency is applied to the winding 20.

In Fig. 3 there is illustrated a modified structure which may be used in the same manner as the structure of Fig. 1 to provide a vibrating member which operates at a constant frequency. In this structure the reed ID and base member [2 may be identical with the components in Fig. 1. A different top support structure, however, is provided which may include a rigid plate 30 positioned to hold a resilient member 3| along the top surface of the reed. The reed is clamped to the base member 12 by a clamp 32 in a manner to provide a point 33 about which the reed Iii vibrates. The clamp 32 holds the reed sufficiently securely to the base member so that the reed must vibrate about the point 33 but yet permits sliding movement of the reed In with respect to the base 12 and the clamp 32. The top structure is arranged so that the resilient material 3! bears against the top surface of the reed firmly enough to prevent vibration of this portion of the reed but presents very little resistance to sliding action of the reed ii] along the support 12. The reed [0 in Fig. 3 can be used in the same manner as reed ID in Fig. 1 in connection with a signaling system in which currents are applied to winding to produce a field which cooperates with the field of the magnet 2| to cause Vibration of the reed when frequency corresponding to the natural frequency of the reed I0 is applied to the winding. The vibration of the reed closes the circuit through contacts 24 and in the same manner as above described.

Known materials which are used as vibrating members, such as spring steel, for example, have a natural tendency to change the frequency of vibration with change of temperature. This is caused by the temperature coefficient of expansion of the material which causes the reed to increase in length with rise in temperature and also to the change in elasticity of the material with temperature. Both of these characteristics result in the natural frequency of vibration of the reed decreasing with rise in temperature. This decrease in natural frequency can be compensated for by decreasing the length of the portion of the reed which is free to vibrate as the temperature increases. This function is accomplished in the structure of Fig. 1 by making the mounting members l2 and I3 of material which has a relatively high temperature coefficient of expansion. By making the members i2 and i3 of material which has a greater coefficient of expansion than the reed If], the clamping edge IE will move out along the reed as the temperature rises causing the portion free to vibrate to be decreased in length. It is apparent that by choosing materials having various coefficients of expansion and by adjusting the length of the reed and the support, it is possible to provide reeds which will vibrate at various frequencies and which will be substantially independent of the temperature at such frequencies. In structures actually tested, reeds made of clock spring steel and support members made of brass were found to be satisfactory. These reeds were arranged to operate at approximately 200 cycles per second with the reed being approximately 3.8 inches long and the support 2 inches long. Tests of these reeds indicated that the frequency response was substantially constant through a range of ap proximately degrees centigrade. This, of course, would cover the temperature range encountered under most any operating conditions.

It is to be pointed out that to provide complete compensation, the length of the portion of the reed free to vibrate does not remain constant as in addition to compensating for the expansion of the reed it is also necessary to compensate for the change in elasticity thereof. Therefore, when using a material in which the elasticity decreases with temperature, the portion free to vibrate must become shorter with increase in temperature to compensate for the natural tendency of the reed to operate at a lower frequency due to the change in elasticity caused by the rise in temperature.

It is seen from the above that there is provided a compensating mounting for a vibrating member which provides substantially constant frequency of vibration through a relatively wide range of temperatures. The reed itself and the components of the mounting are all of very simple and inexpensive construction so that the entire unit can be easily and cheaply constructed. In a tual tests the structure has proven to be completely effective and provides compensation of the accuracy required in most applications, being entirely satisfactory for selective calling systems.

Although I have described certain embodiments of my invention which are illustrative thereof, it is obvious that various changes and modifications can be made therein without departing from the intended scope of the invention as defined in the appended claims.

I claim:

1. A vibrating unit adapted to operate at a. fixed frequency which is substantially independent of the temperature to which the unit is sub jected, comprising a vibrating member having a natural frequency-temperature characteristic and a mounting therefor which is arranged to support said member so that a portion thereof is free to vibrate, said mounting being made of material which expands with increasing temperature so that the configuration of the mounting changes and the portion of said member which is free to vibrate varies with the temperature to which the system is subjected, to thereby compensate for the natural frequency-temperature characteristic of said member,

2. A vibrating unit adapted to operate at a predetermined frequency which does not change substantially with the temperature to which the unit is subjected, comprising a vibrating member having a natural frequency-temperature characteristic and a mounting therefor which is arranged to support said member so that a portion thereof is free to vibrate, said mounting being made of material having such temperature characteristics that the configuration of the mounting changes and the portion of said member which is free to vibrate varies with the temperature to which the system is subjected, and compensates for the natural frequency-temperature characteristic of said member.

3. A vibrating unit adapted to operate at a fixed frequency substantially entirely independently of the temperature to which the unit is subjected comprising, an elongated vibrating memher and a mounting for the same, said mounting including a base to which one end of said member is secured, said. member including a portion adja cent said one end which rests on said base, and means for holding said portion of said member against said base.

a. In a vibrating, unit adapted to operate at a fixed frequency which is substantially indenpendent of the temperature to which the unit is subjected, the method of compensating for the natural frequency temperature charact ristics of the vibrating member which comprises, rigidly securing said member at one end thereof, supporting said member along a portion of its length adjacent said one end so that said portion is restrained from vibration, and varying length of the portion supported in accordance with temperature to compensate for the natural frequency-temperature characteristics of said member,

5. In a vibrating unit adapted to operate at a fixed frequency which is substantially independent of the temperature to which the unit is subjected, the method of compensating for the reduction of the natural fr quency of vibration of the member with increase in temperature which comprises, rigidly securing said member at one end thereof, and supporting said member along a portion of its length adjacent said one end by material which expands with increasing temperature at a greater rate than the material from which said reed is made, so that the portion of the member which is restrained from vibration varies in accordance with temperature to compensate for the natural frequency-temperature characteristics of said member.

6. A vibrating unit adapted to operate at a fixed frequency substantially entirely independently of the temperature to which the unit is subjected comprising, a vibrating reed made of material which expands with increased temperature, and a mounting for said reed including a base on which a portion of said reed rests, means for securing said portion at one end thereof to said base, and means for holding said portion of said reed against said base so that said portion is restrained from vibration, said base being made of material which expands with increase in temperature at a greater rate than the material from which said reed is made, so that said portion of said reed which is restrained from vibration increases with temperature and the natural frequency of the portion of said member which is free to vibrate remains substantially constant.

7. A vibrating unit adapted to operate at a fixed frequency substantially entirely independently of the temperature to which the unit is subjected comprising, an elongated vibrating member made of material which expands with increasing temperature, and a mounting for said vibrating member including a base on which a portion of said member rests, means for securing said portion at one end thereof to said base, and means for holding said portion of said member against said base so that said portion is restrained from vibration, said base being made of material which expands with increase in temperature at a greater rate than the material of said member so that said portion of said member which is restrained from vibration increases with tern-- perature and the length of the portion of the member which is free to vibrate is reduced the proper amount so that the natural frequency of vibration thereof remains substantially at said fixed freouency.

8. A vibrating unit adapted to operate at a fixed frequency substantially independently of the temperature to which the unit is subjected. comprising, an elongated vibrating member, a mounting for said member including an elongated base of lesser length than said member, said member having a first portion thereof resting on said base and a second portion extending beyond said base, means rigidly securing member at one end thereof to one end of said base, and means for holding said first portion against said base in such manner that said first portion is restrained from vibration.

9. A vibrating unit adapted to operate at a fixed frequency substantially independently of the temperature to which the unit is subjected comprising, an elongated vibrating reed, a mounting for said member including an elongated base of lesser length than said reed, said reed having a first portion resting on said base and a second portion extending beyond said base, means rigidly securing said reed at one end thereof to one end of said base, and means for holding said first portion against said base to restrain said first portion from vibration, said reed being made of material such that the natural frequency of vibration thereof is lowered in response to rise in temperature, said base being made of material which expands with the rise in temperature to thereby increase the portion of said reed which is restrained so that the natural frequency of vibration of the portion extending beyond said base remains. substantially constant.

10. A vibrating unit adapted to operate at a fixed frequency substantially independently of the temperature to which the unit is subjected comprising, a vibrating reed, a mountin for said member including an elongated base of lesser length than said reed and having first and second ends, said reecl having a first portion thereof resting on said base, and a second portion extending beyond said base, means rigidly securing said reed at one end thereof to said first end of said base, a rigid top support positioned on said reed, and being coextensive with said base, a spacer positioned between said one end of said reed, and said top support so that said top support engages said reed only adjacent said second end of said base, and a clamp for holding said top support against said reed so that said first portion of said reed is restrained from vibration, said reed being made of material such that the natural frequency of vibration thereof is lowered in response to rise in temperature, said base and said top support being made of material which expands with the rise in temperature to thereby increase the portion of said reed which is restrained so that the natural frequency of vibration of the portion extending beyond said base remains substantially constant.

11. A Vibrating unit adapted to operate at a fixed frequency substantially independently of the temperature to which the unit is subjected comprising, an elongated vibrating reed, a mounting for said reed including an elongated base of lesser length than said reed and having first and second ends, said reed having a first portion resting on said base and a second portion extending beyond said base, means rigidly securing said reed at one end thereof to said first end of said base, a clamp at said second end of said base adapted to hold said reed against said base, resilient means for holding said first portion against said base to restrain said first portion from vibration, said reed being made of material such that the natural frequency of vibration thereof is lowered in response to rise in temperature, said base being made of material which expands with the rise in temperature to thereby increase the portion of said reed which is restrained so that the natural frequency of vibration of the portion extending beyond said base remains substantially constant.

12. A vibrating unit adapted to operate at a fixed frequency substantially independently of the temperature to which the unit is subjected comprising, an elongated vibrating member, a mounting for said member including an elongated base of lesser length than said member, said member having a portion resting on said base and a portion extending beyond said base, means rigidly securing said member at one end thereof to one end of said base, and means for restraining said portion of said member which rests on said base from vibration, said member and said base being made of materials having such coefficients of expansion that said base expands with increasing temperature faster than said member so that the natural frequency of vibration of the portion of said member extending beyond said bas remains substantially constant.

13. A vibrating unit adapted to operate at a fixed frequency substantially independently of the temperature to which the unit is subjected comprising, an elongated vibrating member, a mounting for said member including an elongated base of lesser length than said member, said member having a portion resting on said base and a portion extending beyond said base, means rigidly securin said member at one end to one end of said base, and means for restraining said portion of said member which rests on said base from vibration, said member being made of material which expands with increase in temperature to decrease the natural frequency of vibration thereof and the elasticity of which changes with temperature to further decrease the natural frequency of vibration of said member with increase in temperature, said base being made of material which expands with increase in temperature at a greater rate than said member so that the portion of said member extending beyond said base is reduced with increase in frequency and the natural frequency of vibration thereof remains substantially constant,

14. A vibrating unit adapted to operate at a fixed frequency substantially independently of the temperature to which the unit is subjected comprising, an elongated vibrating member, a mounting for said member including an elongated base of lesser length than said member, said member havim a portion resting on said base and a portion extendin beyond said base, means rigidly securing said member at one end to one end of said base, and means for restraining said portion of said member which rests on said base from vibration, said member being made of material the elasticity of which changes with temperature to decrease the natural frequency of vibration of said member with increase in temperature, said base being made of material which expands with increase in temperature so that the portion of said member extending beyond said base is reduced with increase in frequency and the natural frequency of vibration thereof remains substantially constant.

DANIEL E. NOBLE,

REFERENCES CETED The following references are of record in the le of this patent:

UNI'IED S'IATES PATENTS Number Name Date 4,212 Schneider Sept. 27, 1845 139,912 Morgan June 17, 1873 143,093 Procope Sept. 23, 1873 

